This paper examines assumptions about second language acquisition, bilingualism, and language planning that underlie Singapore's bilingual education policy, noting how the experience in Singapore illuminates current theories in second language acquisition and language planning. In Singapore, English is promoted as the "working language," while Mandarin, Chinese, Malay, and Tamil are considered mother tongues of the major ethnic groups. In the late 1970s, the government adopted a bilingual education policy which requires that all students study their subject matter curriculum in English and all students achieve proficiency in their mother tongue. Singapore's national exams usually show upward trends for all ethnic groups, though there is an achievement gap between the Chinese majority and the Malay and Indian minority groups. Although Chinese students consistently outperform the other groups, and a greater proportion move on to higher education, each ethnic group shows strengths in different areas. Singapore's language policy reflects many common assumptions about language learning (e.g., beginning a second language early leads to higher proficiency). It also reflects many assumptions concerning language planning (e.g., language is a tool that should be carefully chosen for its utility to the national interest). (Contains 38 references.) (SM)